1. Field of the Invention
The present invention relates in general to a variable-width substrate conveyor the width of which is variable, a method of changing the width of such a variable-width substrate conveyor, and a method of matching the widths of two adjacent substrate conveyors. More particularly, this invention is concerned with automatic changing of the width of the substrate conveyor.
2. Discussion of Related Art
A substrate conveyor is provided in various systems and equipment such as an electric-component mounting system, for conveying or feeding a circuit substrate such as a printed-circuit board. The electric-component mounting system is arranged to mount electric components (typically, electronic components) on the printed-circuit board. The substrate conveyor may be a variable-width conveyor. For instance, the variable-width substrate conveyor includes a stationary guide rail, a movable guide rail movable toward and away from the stationary guide rail, a pair of endless belts, and a belt-drive device. The pair of endless belts are guided by the stationary and movable guide rails, respectively, and the circuit substrate is supported at its widthwise opposite sides by straight portions of the endless belts. The endless belts are rotated by the belt-drive device, so that the circuit substrate is fed by the endless belts while the circuit substrate is guided at its side edges by the pair of guide rails.
The width of the variable-width substrate conveyor is changed depending upon the specific width of the circuit substrate to be fed. The width of the substrate conveyor is changed by changing the distance between the pair of guide rails. Conventionally, the width of the substrate conveyor is automatically changed by a movement of the movable guide rail by a width changing device which uses a servomotor as its drive source, for example. The servomotor is an electric motor whose operating angle can be accurately controlled, so that the movable guide rail can be accurately moved to a position at which the width between the two guide rails corresponds to the width of the circuit substrate.
However, the servomotor is expensive and inevitably increases the cost of manufacture of the variable-width substrate conveyor. Further, the use of the servomotor does not necessarily assure a sufficiently high degree of accuracy of positioning of the movable guide rail. Where a single servomotor is used to rotate a plurality of feedscrews arranged in the longitudinal direction of the movable guide rail, for example, the movable guide rail may not be positioned with a sufficiently high degree of accuracy, even if the operating angle of the servomotor itself is accurately controlled. Namely, a rotary motion of the servomotor is transmitted to the plurality of feedscrews through a motion transmitting device including chains and sprockets. The accuracy of motion transmission from the servomotor to the feedscrews may be deteriorated due to backlashes and other factors of the motion transmitting device, so that the positioning accuracy of the movable guide rail may be deteriorated.